We have made this successfully using a whole front leg of a pig.
The part of a hog closest to the shoulder is called the Boston
shoulder roast or sometimes a blade roast or pork butt. The lower
section of the front leg is called the picnic shoulder.

Heat a little olive oil in a skillet and brown the pork on all
sides. Transfer the meat to a Dutch oven or other suitable oven pan.

Use a vegetable peeler or sharp pairing knife and remove the zest from 1
small orange. Use the juice from the remainder of the orange plus enough
additional juice to make up 1 cup orange juice.

Cover pot and cook in a 325oF oven for 1 hour.
Turn pork over and braise for 30 additional minutes.
Check for adequate liquid in the bottom of the pan throughout the
cooking process and top up with additional orange juice if needed.

Peel the celeriac and cut it into 1-inch chunks, keeping them in
lemon water until ready to use. Add the celeriac to the pork and
cook an additional 30 minutes.

Turn pork over and braise for another hour, or until pork and celeriac
are done. The pork should be 160oF on an internal meat
thermometer.